After his father's death his mother married a friend of Pericles so he was politically connected to both the oligarchy and democracy. After the Peloponnesian War, his mother's brother and uncle tried to persuade him to join in the oligarchical rules of Athens. Instead, Plato joined his two older brothers in becoming a student of Socrates. Socrates forced them to challenge then to examine their ideas and beliefs critically, which was annoying and antagonizing many in the process. Socrates seems to have adopted as his own the motto of the Delphic Oracle, "Know thyself"; and, while trying to dissociate himself from the sophists' brand of instruction for hire, he taught his students that, "it is the greatest good for a man to discuss virtue every day and those other things about which you hear me conversing and testing myself and others, for the unexamined life is not worth living."
Plato was an opponent of the relativism and scepticism of the Sophists; but, like them he focused on values rather than on physical science. Aristotle credits Socrates with emphasizing moral questions and precise definitions; and Plato surely absorbed these lessons.
Plato was no friend of the Thirty Tyrants, who's reign (404-403 BC) lasted only 8 months, but he also was not a friend of the Athenian democracy when it was restored. He alienated them by him method of critical interrogation. In 399 BC he was brought to trial with the capital crimes of religious impiety and corruption of youth, convicted, and sentenced to death. His friends offered to pay a fine instead of the death penalty. As Plato tells us in the Seventh Letter after Socrates' death, he became disenchanted with all existing political regimes, and felt that the only salvation of politics would require that "either true and genuine philosophers attain political power or the rulers of states by some dispensation of providence become genuine philosophers."
About 387 BC, Plato founded a school in Athens, in a grove sacred to the demigod Academus, called the Academy (which is where we get the word academics from today). It was, in effect, a university of higher learning, which included physical science, astronomy, and mathematics, as well as philosophy. In addition to presiding over the Academy, Plato delivered lectures, which were never published.
In 367 BC Dionysius died and was succeeded by his teenage son, Dionysius II, whose uncle, Dion, was a close friend to Plato. Dion invited Plato to come a school Dionysius for his future kingship. Plato, seeing that this was a way for him to complete his goal for a philosopher king decided to travel to Sicily and take control of the boy's studies. Dionysius II later had a fight with Dion, and exiled him, Plato was unable to convert the boy to philosophy and returned the Athens, where Dion had established residence. Plato continued correspondence with Dionysius II, and tried to have him reconcile with Dion. Dionysius II lured Plato into a trap, by telling him that he wanted to become a philosopher. Plato was trapped in Syracuse until 360. Where he traveled back to Athens and continued to function as president of the Academy. He died in 347 BC, at about the age of eighty.